Electrical filter circuit device



P 1934- P. E. EDEL-MAN ELECTRICAL FILTER CIRCUIT DEVICE Filed April 18. 1928 mm m W M mw WWW Mm Patented Sept. 18, 1934 "NITED STATES ism PATENT PI-ICE Philip E. Edelman, Chicago, 111., assignor, by mesne assignments, to Robert- T. Mack, trustee,

Chicago, Ill.

Application April 18, 1928, Serial No. 270,835

1 Claim. (Cl. 178-44) My present invention relates to electrical filter circuit elements intended to be selective in current passing action by discriminating between different forms of electrical current, such as example as are combined into a filter circuit for a radio power supply unit. An object of the present invention is to improve the selective discrimination between alternating current and direct current passed thru the filter elements and increase the efficiency of filtration. A further object is to reduce the cost of such filtering devices. A further object is to proportion absorption energy losses in said filter circuit elements to be greater for components resulting from alternating current fiow therethrough, than for direct flowing current. Various other objects will presently appear and are more particularly pointed out, it being obvious to anyone skilled in the art that various changes and modifications may be made according to my idea and within the scope of the appended claim.

In order to obtain an effective filtering action, as for example in a plate current supply device, I have conceived and determined that it is surprisingly advantageous to purposely introduce energy losses in the filtering elements provided that such losses are purposely proportioned to be greater when caused by fluctuating or alternating current excitation than when caused by direct current. The reason'for this is that ripple current represents energy and absorption of a portion of such energy reduces the quantity of ripple energy. When merely a resistance is lumped or distributed in a filter circuit, only a slight improvement is had, and at the expense of direct current energy which is also consumed as heat in the resistance. By a proper proportioning and predetermined introduction of eddy current losses, same can be rendered negligible when set up by direct flowing current but relatively large when caused by ripple current flow or alternating current.

I show an exemplification of my invention in the accompanying drawing in which the figure shows a diagram, partly sectioned, illustrating a conventional electrical filter circuit characterized by my improvements therein.

A transformer 1, actuated by a source of alternating current 2, feeds a rectifier 3 which supplies current to the input terminals 24, 25 of the electrical filter 26, from which output current may be had at terminals 10, 12, and 11.

Two choke coils 4, 5, respectively are series connected to rectifier 3. Condenser elements 6 and 7 are shunt connected as shown. A resistance 9 tapped at 12 is also shunt connected across terminals 10 and 11. A condenser 8 is shunted around a portion of resistance 9 between terminals 12 and 11.

The aforesaid conventional filter circuit is characterized by the following improvements.

(1) The choke coiZ.--Choke coil 4, for example, 0 is constructed with its coil winding 17 bounded by a core consisting of two air spaced pieces of cast iron or soft steel, 13, 13A, whereby air gaps 18, 19, 20 are proportioned therebetween. Each casting 13 or 13A is similar, and 13 has mounting lugs 15 formed integral therewith and including holes 16. Holes 14 may also be formed in casting 13 for fastening purposes. The cross section of each leg 29, 30, 31 of casting 13 may be square or any other desired shape, with the area of leg 30 7 approximately twice that of either 29 or 31. The dimension e of leg 30 is proportioned according to the dimension d of coil winding 17 so that e is greater than d.

Coil winding 17 may have any desired shape but preferably is made with length at least twice as great as outside diameter in order that the resistance of winding 1'7 may be small for a given number of turns thereof. Core 13 is grounded to terminals 25 and 11 by wire 27. Heretofore so 'it has been the practice in this art to employ laminations to form core pieces such as core portion 13. This is costly in requiring numerous die stamped pieces to be assembled with separate mounting means, and fails to introduce eddy current losses which are preponderantly greater for alternating current excitation, as is the case for solid core 13 proportioned and constructed as set forth.

I prefer to use a cast iron material for core member 13 though soft steel or an-alloy containing nickel is also suitable. The cast iron should have approximately 4 per cent carbon of which .5 per cent is in combined form, and be relatively low in silicon, manganese, phosphorus, sulphur or other impurities. It is permissible to use iron with as much as 2 per cent silicon and a very small proportion of aluminum, but the other alloy materials mentioned should be kept down to a minimum. Such a cast iron is capable of introducing iron losses desired when proportioned as set forth, whereby relatively large-losses are caused by alternating or pulsating current fiow thru coil winding 17.

The plurality of air gaps 11, 19, 20 tend to prevent saturation of core member 13, and should be of length approximately 1/80 inch.

In assembling the choke coil 4, the winding 1'7, prepared as is customary in the art, is slipped over one core member 13 and the similar integral no Choke coil 5 is similarly constructed but preferably its air gaps 21, 22, 23 are adjusted to approximately one half of the length used for air gaps 18, 19, 20 of choke coil 4. Thus, whereas choke coil l tends to have lower impedance than choke coil 5 for a relatively small current flow thru coils 17 of member a and 32 of member 5,.

the reverse becomes true for larger current flow thru said coils, as controlled by the aforesaid difiering air gap lengths. Core piece 33 is similar to core piece 13 and is grounded by wire 28 to terminals 25 and 11. This ground connection via 27 or 28 serves the purpose of using the inherent capacity between windings 17 or 32 and core pieces 13 or 33 respectively as a by-pass shunt for higher frequency currents or harmonics arising in coils 17 and 32, via wires 27, 28 to termiwalls 25 and 11. Such high frequency currents may for example arise from rectifier 3.

It may be remarked that the essentials of an emcient choking coil element have been thereby, as set forth, greatly simplified with fewer parts and more efiective results, eliminating high frequency current components and selectively ab- .sorbing ripple current energy in the form of eddy currents in core pieces 13, 13a, 33, 33a as iron losses, preponderantly greater when caused by alternating current than when set up by direct flowing current. A predetermined proportionment and novel combination of the elements produces the new and useful result sought.

(2) Condenser elements.To further selectively absorb ripple current energy I prefer to provide construction of condensers 6, 7, and 8, specially proportioned therefor.

Thus, as illustrated for condenser 6, a container 37 holds positive dielectric coated plates 24 spaced from negative plates 35 by thin fabric spacers 36 impregnated with a new electrolyte material substantially free from water and having the property of absorbing more energy from alternately fiowing current than from direct fiowing current applied thereto. This electrolyte material in spacers 36 is prepared by dissolving powdered gum arabic in hot pure glycerine, a proportion of ounce of the gum arabic to 1 1b. of glycerine being suitable.

By stirring the mixture, a clear solution of gum arabic in glycerine is had, somewhat brown in color. The. glycerine, which is a poor conductor of electricity of itself, with relatively high dielectric constant, is rendered selectively a conductor of electricity by the dissolved gum arabic. Gum arabic comprises a material containing salts of organic acid of very high molecular weight, possessing marked rotation effect of the plane of polarized light, effective osmotic pressure, and the further property of rendering the glycerine harmless to the plates 34 and 35. It is known that whereas glycerine tends to separate OH ions under the action of electrical current so that plates 34 and 35, if made from aluminum, are attacked, such is not the case after the gum arabic is dissolved therein. The action is markedly difierent than when aqueous mixtures are used with glycerine or when inorganic' salts are mixed with glycerine or glycerine and water. Reference is made to my copending application for U. S. Letters Patent filed April 12, 1928 for Polarized electrical couple Serial No. 269,615 (Patent 1,773,665, Aug. 19, 1930) in which a suitable mode of pre= paring electrode plates 34, 35 is set forth. The construction set forth herein difiers as specified in the non-aqueous electrolyte material contained in spacers 36 proportioned for the purpose here-= in set forth. Other organic gums or compounds may be dissolved in the glycerine but gum trag-= acanth, for example, renders the mass very thick.

Salts of the heavy organic acid comprised in said gum arabic become dissociated in said glycerine, so that free ions are dispersed therein.

The aforesaid solution of gum arabic in glycerine appears to be stable and unvarying in action and introduces sufiicient resistance or heat loss in said material characterized with the prop-= erty desired as set forth, there being little or no such energy losswhen pure direct current is applied to condenser 6. Similar construction may be employed for condensers 7 and 8 as is obvious.

The action is thus purposely proportioned to introduce energy absorption for energy represented in ripple current, due to incomplete rectification by rectifier 3, without materially increasing loss of energy represented by direct current output of rectifier 3. If for example, coil 17 were wound with resistance wire, the same effect would not be attained because the loss would be increased for direct current fiow as well as for alter nating current fiow therethru. For certain purposes it may serve to use either ordinary condensers with the circuit otherwise prepared as set forth for Figure 26, representing the filter circuit, or it may be permissible for some purposes to employ ordinary choke coils with the filter 26 otherwise as shown, but the joint action of both expedients effectively combines for the purpose set forth producing the new result set forth.

The filtering action difiers over that of the prior art in that, beyond the regular expected filtering action of improved efiqciency, there is the additional filtering action on residual or remaining ripple current by the selective energy losses obtained as set forth. Thus, whereas ordinary filters of this general type pass considerable ripple current at reduced intensity, the improved combination set forth, with purposely proportioned elements constructed to absorb energy represented in ripple currents, substantially completely filters the input supply to a steady flow of direct current free from ripples at output terminals 10, 11, 12. When such a filter is used as a plate supply for a radio set, the marked improvement set forthcan be noticed in the improved quality of reproduction obtainable from said radio set.

It may be remarked that the phasing obtained by the combination shown is in proper relation for maximum absorption of ripple current by said filter, the actions of the structures in elements 4, 5, 6, and 7 cooperating cumulatively because of such combination for the result stated.

I claim:

An electrical filter including a choke coil and a condenser in order to substantially pass direct current and reject alternating current supplied thereto, characterized by the fact that residual ripple current is dissipated by purposely proportioning solid cast core sections and a cooperating winding, and an air gap intermediate said core sections to form said choke coil, whereby iron losses in said sections are increased with respect to the values of said residual ripple current.

PHILIP E. EDELMAN; 

